Probability

I think you ask for the least number of terms that you have to study and you can answer all the 5 questions to get full mark in all cases.
You at least study 108-(15-10) = 98 terms. Because if you are the unluckiest, the 10 terms you have not studied are selected among the 15 questions, and you can still choose the remaining 5 questions you have studied to answer .

Note: if you study 97 terms, i.e. you have not studied 11 terms, and there is a possibility that all the 11 terms are included in the 15 questions, and you cannot get full mark.

Form my point of view,
perhaps it is as following:-

1/108*1/107*1/106*1/105*1/104*1/103*1/102*1/101*1/100*1/99*1/98*1/97*1/96*1/95*1/94*1/15*1/14*1/13*1/12*1/11

I donot calculate the answer and it must be taken my time to them.

So hope someone calculate it.

2007-04-20 13:12:00 補充：
或然率的計法：第1個被選的問題的機率108個中選得是為1/108第2個被選的問題的機率108-1=107個中選得是為1/107(每選一次其實便少了1個)第3個被選的問題的機率108-2=106個中選得是為1/106....................第15個被選的問題的機率108-14=94個中選得是為1/94這便是首輪的機率的排列法：1/108*1/107*1/106*1/105*1/104*1/103*1/102*1/101*1/100*1/99*1/98*1/97*1/96*1/95*1/94

2007-04-20 13:12:10 補充：
第二輪自選的的機率：第一個由15個被選的問題中選取：1/15第二個由14個被選的問題中選取：1/14第三個由13個被選的問題中選取：1/13第四個由12個被選的問題中選取：1/12第五個由11個被選的問題中選取：1/11因為是二組數值排列，算式便是如此：1/108*1/107*1/106*1/105*1/104*1/103*1/102*1/101*1/100*1/99*1/98*1/97*1/96*1/95*1/94*1/15*1/14*1/13*1/12*1/11

i guess...if really even distrubution..u should study 5/15 *108 ..i.e. 36